EP0936279B1 - Thick cold rolled steel sheet excellent in deep drawability and method of manufacturing the same - Google Patents

Thick cold rolled steel sheet excellent in deep drawability and method of manufacturing the same Download PDF

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Publication number
EP0936279B1
EP0936279B1 EP98935327A EP98935327A EP0936279B1 EP 0936279 B1 EP0936279 B1 EP 0936279B1 EP 98935327 A EP98935327 A EP 98935327A EP 98935327 A EP98935327 A EP 98935327A EP 0936279 B1 EP0936279 B1 EP 0936279B1
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EP
European Patent Office
Prior art keywords
steel
rolling
sheet
weight
rolled
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Expired - Lifetime
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EP98935327A
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German (de)
English (en)
French (fr)
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EP0936279A4 (en
EP0936279A1 (en
Inventor
Yoshikazu Technical Res. Lab. Kawasaki KAWABATA
Kaneharu Tech. Res. Lab. Kawasaki OKUDA
Kei Tech. Res. Lab. Kawasaki Steel Corp. SAKATA
Takashi Tech. Res. Lab. Kawasaki OBARA
Atsushi Tech. Res. Lab. Kawasaki OGINA
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JFE Steel Corp
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JFE Steel Corp
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0436—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing

Definitions

  • the present invention relates to cold-rolled sheet steel favorable to use for compressor covers, oil pans for vehicles and others, in particular, to that with good deep drawability having a thickness of not smaller than 1.2 mm, and also to a method for producing it.
  • JP-A Japanese Patent Application Laid-Open
  • JP-A Hei-3-150916 they say that the sheet steel produced has an r value of about 2.9.
  • the thickness of the slab to be rolled must be at most about 200 mm or so, and the reduction ratio in the rough hot-rolling step must be at least 85 % in order that the steel grains could be sufficiently fined in the lubricative warm-rolling step prior to the final rolling step for finishing.
  • the thickness of the sheet bar to be rolled shall be at most about 30 mm or so.
  • the thickness of the sheet bars to be rolled shall be at most about 30 mm or so in view of the coiling ability of the sheet bar coiler to be used therein.
  • the thickness of the sheet bars capable of being rolled in the conventional process could be at most about 30 mm or so. Therefore, according to the conventional rolling process, it is extremely difficult to obtain cold-rolled sheet steel having a thickness of not smaller than 1.2 mm, while satisfying the combination of the reduction ratio in the lubricative warm-rolling step of being not lower than 90 % and the reduction ratio in the cold rolling step of being not lower than 75 %. Even if the reduction ratio in the lubricative warm-rolling step could be at most 86 % and that in the cold rolling step be at most 75 % under various conditions, the r value of the actually rolled sheets could be at most about 2.6 or so.
  • prior art WO-A-98 28 457 forms part of the state of the art in accordance with Article 54(3) EPC.
  • This prior art document discloses a steel sheet having a thickness of 1.20 after cold rolling and an r-value of 2.90. Further, during the process of producing this known steel sheet, the steel sheet is recrystallization annealed at a temperature of 910°C for 40 seconds.
  • one object of the present invention is to provide cold-rolled thick sheet steel having a thickness of not smaller than 1.2 mm and having an r value of not lower than 2.95,
  • Another object of the invention is to provide a practicable method for producing cold-rolled thick sheet steel having a thickness of not smaller than 1.2 mm and having an r value of not lower than 2.95.
  • the invention provides a method: for producing a thick cold-rolled steel sheet as defined in claim 1 and a steel sheet as defined in claim 3.
  • a preferred embodiment of the inventive method is defined in the dependent claim 2.
  • Fig. 1 shows a method for measuring the shear strain of sheet steel.
  • a slit was formed in a sheet steel sample in the direction vertical to the rolling direction, and from the degree of inclination, ⁇ , of the slit in the rolled sample, obtained was the shear strain, (1 + ⁇ ) 2 tan ⁇ , in which ⁇ indicates the reduction ratio.
  • the shear strain was measured at 50 points at regular intervals in the direction of the thickness of the sheet sample, and the data measured were averaged in the thickness direction to obtain the mean shear strain.
  • Fig. 2 to Fig. 5 show the data which we obtained in our experiments.
  • Fig. 2 is a graph showing the influence of the mean shear strain of lubricative warm-rolled sheet steel and the reduction ratio for the sheet steel, on the r value of the cold-rolled sheet steel. From Fig. 2, it is known that when the reduction ratio in the lubricative warm-rolling step is not lower than 65 % and when the mean shear strain of the lubricative warm-rolled sheet steel is not larger than 0.06, then the r value of the cold-rolled sheet steel is significantly increased.
  • Fig. 3 is a graph showing the shear strain of the lubricative warm-rolled sheet steel that varies in the direction of the thickness of the sheet steel. As in Fig.
  • the shear strain is concentrated within the region of about 0.5 mm from the surface layer, irrespective of the thickness of the finishing hot-rolled sheet steel, and that the mean shear strain of the hot-rolled sheet steel could be reduced if the sheet steel could be controlled to have a suitably large thickness.
  • Sheet steel capable of being produced in the prior art to have a thickness of 1.2 mm or more could have an r value of at most 2.6, and its drawability is not always satisfactory.
  • the object of the present invention is to provide thick cold-rolled sheet steel having a thickness of not smaller than 1.2 mm and having an r value of 2.95 or more.
  • the r value of 2.9 is the highest for sheet steel having a thickness of smaller than 1.2 mm.
  • r (r 0 + 2r 45 + r 90 )/4 wherein r 0 , r 45 and r 90 each indicate the Lankford value of sheet steel in the rolling direction, in the direction at an angle of 45° relative to the rolling direction, and in the direction at an angle of 90° relative to the rolling direction, respectively.
  • C is as smaller as possible for better deep drawability of sheet steel.
  • C in steel in an amount of not larger than 0.008 % by weight would not have any significant negative influences on the workability of the steel. Therefore, the C content of steel in the invention is defined to be not larger than 0.008 % by weight, but preferably not larger than 0.002 % by weight.
  • Si not larger than 0.5 % by weight.
  • the amount of Si to be in the steel of the invention is defined to be not larger than 0.5 % by weight, but preferably smaller than 0.1 % by weight.
  • Mn not larger than 1.0 % by weight.
  • Mn acts to reinforce steel, and a necessary amount of Mn is added to steel in accordance with the intended strength of the steel.
  • adding too much Mn to steel in an amount of larger than 1.0 % by weight will have some negative, influences on the deep drawability of the steel. Therefore, the amount of Mn to be in the steel of the invention is defined to be not larger than 1.0 % by weight, but preferably from 0.05 to 0.15 % by weight.
  • the amount of P to be in the steel of the invention is defined to be not larger than 0.15 % by weight, but preferably smaller than 0.01 % by weight.
  • S is as smaller as possible for better deep drawability of sheet steel.
  • S in steel in an amount of not larger than 0.02 % by weight would not have any significant negative influences on the workability of the steel. Therefore, the S content of steel in the invention is defined to be not larger than 0.02 % by weight, but preferably smaller than 0.008 % by weight.
  • Al from 0.01 to 0.10 % by weight.
  • Al is for deoxidation of steel, and is added to steel for the purpose of increasing the yield of elements for producing carbonitrides in steel.
  • Al added to steel in an amount of smaller than 0.01 % by weight will be ineffective.
  • the amount of Al to be added is defined to fall between 0.01 and 0.10 % by weight, but preferably between 0.02 and 0.06 % by weight.
  • N not larger than 0.008 % by weight.
  • N is as smaller as possible for better deep drawability of sheet steel.
  • N in steel in an amount of not larger than 0.008 % by weight would not have any significant negative influences on the workability of the steel. Therefore, the N content of steel in the invention is defined to be not larger than 0.008 % by weight, but preferably smaller than 0.004 % by weight.
  • Ti is an element for forming carbonitrides in steel. This acts to reduce the solute C and the solute N in steel to be subjected to lubricative warm-rolling or to cold-rolling, and assists the orientation of grains predominantly in the site of ⁇ 111 ⁇ , while steel having been hot-rolled or cold-rolled is annealed, to thereby increase the r value (mean value) of the rolled sheet steel.
  • Ti added to steel in an amount of smaller than 0.035 % by weight will be ineffective.
  • the amount of Ti to be added is defined to fall between 0.035 and 0.20 % by weight, but preferably between 0.04 and 0.08 % by weight.
  • Nb from 0.001 to 0.015 % by weight.
  • Nb is also an element for forming carbonitrides in steel. Like Ti, this acts to reduce the solute C and the solute N in steel to be subjected to lubricative warm-rolling or to cold-rolling, and assists the orientation of grains predominantly in the site of ⁇ 111 ⁇ , while steel having been warm-rolled or cold-rolled is annealed. In addition, Nb acts to produce a fine texture of steel which is subjected to lubricative warm-rolling, and assists the orientation of grains predominantly in the site of ⁇ 111 ⁇ in the next step of annealing the rolled sheet steel. As having such capabilities, Nb is added to steel for the purpose of increasing the r value (mean value) of the rolled sheet steel.
  • the solute Nb in steel is further effective for accumulating the strain in the hot-rolled sheet steel, while promoting the growth of the texture of the hot-rolled sheet steel.
  • Nb added to steel in an amount of smaller than 0.001 % by weight will be ineffective.
  • the amount of Ti to be added to steel in the invention is defined to fall between 0.001 and 0.015 % by weight, but preferably between 0.01 and 0.015 % by weight.
  • B is an element effective for improving steel to be non-brittle in secondary working, and is optionally added to steel.
  • B added to steel in an amount of smaller than 0.0001 % by weight will be ineffective.
  • the amount of B to be added to steel in the invention is defined to fall between 0.0001 and 0.01 % by weight, but preferably between 0.0002 and 0.0012 % by weight.
  • the texture of the rolled and annealed sheet steel is oriented in the site of ⁇ 111 ⁇ .
  • the sheet steel is much more oriented in the site of ⁇ 111 ⁇ , thereby having an increased mean r value.
  • the elements C, N, S, Ti and Nb in the steel are so defined that they satisfy the requirement of 1.2(C/12 + N/14 + S/32) ⁇ (Ti/48 + Nb/93) .
  • Ti and Nb are added to steel, which are more than the equivalent amounts of C and N in the steel, so that neither solute C nor solute N exists in the steel prior to the lubricative warm rolling step.
  • sheet bars that are sufficiently thick could be prepared, thick cold-rolled sheets having an r value of not smaller than 2.95 could be produced from them, not only according to the method of the present invention but also according to the method disclosed in JP-A Hei-3-150316 or the like. In fact, however, the largest thickness of sheet bars is limited for the two reasons mentioned below, and thick cold-rolled sheets of steel having an r value of not smaller than 2.9 could not be produced in any prior art technique.
  • the reduction ratio in rough hot-rolling must be at least 85 %, and that the uppermost limit of the thickness of slabs is at most 200 mm or so in view of the capabilities of ordinary continuous casting lines and ordinary rough hot-rolling apparatus. Therefore, the uppermost limit of the thickness of sheet bars shall be at most 30 mm or so.
  • the uppermost limit of the coiling ability of the sheet bar coiler to be used in ordinary continuous rolling lines is generally at most 30 mm or so. This is because the secondary moment of the cross section of sheet steel is proportional to the third power of the thickness of the sheet steel, and because, in the present invention, since the coiling temperature for the sheet bar coiler is low or is around the Ar 3 transformation point of the steel so that the deformation resistance of the sheet bar being coiled is large, too thick sheet bars are difficult to coil and their mechanical properties will be worsened while they are forcedly coiled.
  • the uppermost limit of the thickness of sheet bars capable of being actually worked in practical production lines is to be at most around 30 mm or so.
  • the conventional method for producing sheet steel having an r value of not smaller than 2.9 in which the reduction ratio for rough hot-rolling to be effected at a temperature falling between 600°C and the Ar 3 transformation point of steel is higher than 90 % and the reduction ratio for cold-rolling is not lower than 75 %, it is difficult to produce thick cold-rolled sheet steel having a thickness of larger than 0.75 mm.
  • the reduction ratio for finishing hot-rolling is lowered in accordance with the thickness of the cold-rolled sheet, the r value of the sheet is also lowered.
  • the reduction ratio for finishing hot-rolling when the reduction ratio for finishing hot-rolling is 86 %, the cold-rolled sheet could have an r value of around 2.6 or so.
  • the present inventors have further studied and, as a result, have found that, when the reduction ratio for lubricative warm-rolling is further lowered, then the r value of the cold-rolled sheet is rather increased as opposed to the conventional knowledge.
  • the reason for the result of the invention is because the reduction in the r value of the rolled sheet steel due to the decrease in the reduction ratio for lubricative warm rolling was well compensated for by the increase in the r value of the rolled sheet steel due to the decrease in the mean shear strain of the thick hot-rolled sheet. This is supported not only by the increase in the r value of the cold-rolled sheet but also by the increase in the r value of the pre-annealed sheet bar.
  • the reduction ratio for lubricative warm rolling is lowered to a certain degree, it is believed that the reduction ratio for cold rolling could be increased by the lowered degree of the reduction ratio for the previous lubricative warm rolling, thereby resulting in that, when the reduction ratio for the lubricative warm rolling to be effected at a temperature falling between 600°C and the Ar3 transformation point of steel is 85 % or lower, then the r value of the cold-rolled sheet steel is rather increased.
  • the reduction ratios in both lubricative warm rolling and cold rolling could not be satisfactorily high, for example, where the reduction ratio for cold-rolled sheets is to be lower than 96.5 % relative to the starting sheet bars, the reduction ratio for lubricative warm rolling is lowered to be lower than 85 % and the thickness of the hot-rolled sheets is increased, whereby the r value of the cold-rolled sheets is extremely increased.
  • the mean shear strain of the hot-rolled sheet is to be not larger than 0.06 after the lubricative warm-rolling step.
  • the texture of steel must be oriented in the site of ⁇ 111 ⁇ after the sheet bars are hot-rolled and pre-annealed.
  • the sheet bars shall have fine and uniform texture prior to being subjected to lubricative warm rolling, and that a large amount of strain is accumulated as uniformly as possible in the hot-rolled sheets while the sheets are hot-rolled for finishing, to thereby orient the texture of the sheets predominantly in the site of ⁇ 111 ⁇ while the sheets are pre-annealed.
  • the rough hot-rolling of steel slabs must be finished at a temperature just above the Ar 3 transformation point of steel, in order that the texture of the hot-rolled sheets could be fine and uniform before the sheets are subjected to the next lubricative warm rolling, and that the ⁇ transformation could occur in the sheet just before the lubricative warm rolling step.
  • the temperature at which the rough hot-rolling is finished is higher than 950°C, the texture of the hot-rolled sheet being transformed will be restored to its original condition or the grains will grow in the texture during the step where the sheet is cooled to its Ar3 transformation point at which the ⁇ transformation occurs in the sheet, whereby the texture of the sheet will be rough and uneven before the sheet is hot-rolled for finishing in the next step. Therefore, the rough hot-rolling must not be effected at such high temperatures of higher than 950°C.
  • the reduction ratio for the rough hot-rolling must be at least 85 % in order that the texture of the hot-rolled sheet bars could be fine.
  • the finishing hot-rolling step In the finishing hot-rolling step, a large amount of strain is accumulated in the hot-rolled sheets. Therefore, the finishing hot-rolling must be effected in a warm condition at a temperature not higher than the Ar 3 transformation point of the steel. If the finishing hot-rolling is effected at a temperature higher than the Ar 3 transformation point of the steel, the ⁇ transformation will occur during the hot-rolling whereby the strain in the steel is released, or the texture of the hot-rolled sheet will be randomized. If so, the texture of the sheet could not be oriented predominantly in the site of ⁇ 111 ⁇ in the next annealing step. On the other hand, however, if the finishing hot-rolling temperature is lower than 600°C, the hot-rolling requires greatly increased rolling loads, which are impracticable.
  • the warm-rolling In order to uniformly accumulate a large amount of strain in the warm-rolled sheets, the warm-rolling requires lubrication. If no lubrication is applied to the warm-rolling step, any additional but unfavorable shearing force will be imparted to the surface part of the sheet being rolled, due to the friction force between the roll and the surface of the sheet. If so, the texture of the sheet will be oriented not in the site of ⁇ 111 ⁇ after having been hot-rolled and annealed, whereby the r value of the cold-rolled sheet is lowered.
  • the reduction ratio for the lubricative warm-rolling is defined to be not lower than 65 % so that the thickness of the hot-rolled sheet could be at least 5 mm.
  • the thickness of the hot-rolled sheet is not smaller than 6 mm.
  • the texture of the sheet having been hot-rolled and annealed is oriented predominantly in the site of ⁇ 111 ⁇ .
  • the hot-rolled sheet having a lowered mean shear strain is heated at a temperature falling between 700 and 920°C for recrystallization prior to being cold-rolled.
  • the texture of the sheet can be oriented in the site of ⁇ 111 ⁇ .
  • the heating temperature in the step is higher than 920°C, the ⁇ transformation will occur to randomize the texture of the sheet.
  • the annealing may be effected either in box annealing or continuous annealing.
  • the ferrite grains in the sheet are made fine prior to the cold-rolling step. More preferably, for this, the annealing is effected under the condition under which the ferrite grains in the annealed sheet could be not larger than 50 ⁇ m in size.
  • the reduction ratio for the cold rolling in the method of the invention must be indispensably at least 65 % or more, in order that the texture of the cold-rolled sheet could be well grown and that the r value of the cold-rolled sheet could be well high.
  • the reduction ratio for the cold rolling of 85 % or larger will be impracticable, since the loads to the rolling lines shall be too great.
  • Recrystallization annealing finishing annealing
  • the cold-rolled sheet steel After the cold-rolling step, the cold-rolled sheet steel must be annealed for recrystallization.
  • the annealing may be effected either in box annealing or continuous annealing, in which, however, the heating temperature shall fall between the recrystallization temperature of the steel. That is, the cold-rolled sheet is annealed in high-temperature continuous annealing at a temperature falling between 830°C and 900°C. Preferably the cold-rolled sheet is annealed for a period of from 20 to 60 seconds.
  • the annealed sheet steel may be temper-rolled for correcting its shape and for controlling its surface roughness.
  • the cold-rolled sheet as obtained according to the method mentioned above can be used as a substrate to be worked and surface-treated.
  • the surface treatment includes galvanization (zinc-plating), tin-plating, enameling, etc.
  • a steel sample having the composition No. 1 shown in Table 1 was subjected to rough hot-rolling, finishing hot-rolling, then pickling, pre-annealing, cold-rolling and finishing annealing under the conditions indicated in Tables 2 and 3.
  • Precisely, for the finishing hot-rolling, used was a 7-stage tandem rolling machine equipped with rolls having a radius of 370 mm.
  • the friction coefficient in the finishing hot-rolling step was from 0.2 to 0.25 in every stand.
  • the mean shear strain in the hot-rolled sheet was obtained according to the method mentioned below.
  • a slit (cutting) of 1 mm (width) x 20 mm (depth) was formed in a slab to be rolled, at its center relative to the widthwise direction of the slab, and in the direction vertical to the rolling direction of the slab, and the slab was hot-rolled (finishing hot-rolling), whereupon the shear strain of the finishing-hot-rolled sheet was obtained from the deformation of the slit.
  • the slab with the slit was hot-rolled (rough hot-rolling) to obtain the shear strain of the rough hot-rolled sheet in the same manner as above.
  • the value of the shear strain of the rough-hot-rolled sheet was subtracted from that of the finishing-hot-rolled sheet to obtain the shear strain of the finishing-hot-rolled sheet from the starting sheet bar.
  • the measurement was effected in different points that vary relative to the thickness of each sheet.
  • the data thus obtained were averaged relative to the thickness of the sheet to obtain the mean shear strain of the sheet.
  • the mean shear strain of each finishing-hot-rolled sheet thus obtained in the manner noted above is shown in the following Tables.
  • the present invention provides thick cold-rolled sheet steel with excellent deep drawability, which has an r value of not smaller than 2.95 and a thickness of not smaller than 1.2 and which is produced on an industrial scale.
  • the present invention has made it possible to produce thick cold-rolled sheet steel having a high r value, which, in fact, could not be produced in conventional rolling methods.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)
  • Metal Rolling (AREA)
EP98935327A 1997-08-05 1998-08-03 Thick cold rolled steel sheet excellent in deep drawability and method of manufacturing the same Expired - Lifetime EP0936279B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP21053397 1997-08-05
JP9210533A JPH1150211A (ja) 1997-08-05 1997-08-05 深絞り加工性に優れる厚物冷延鋼板およびその製造方法
PCT/JP1998/003443 WO1999007907A1 (fr) 1997-08-05 1998-08-03 Plaque d'acier epaisse, laminee a froid, ayant une excellente capacite d'etirage, et son procede de fabrication

Publications (3)

Publication Number Publication Date
EP0936279A1 EP0936279A1 (en) 1999-08-18
EP0936279A4 EP0936279A4 (en) 2004-04-21
EP0936279B1 true EP0936279B1 (en) 2005-11-02

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EP98935327A Expired - Lifetime EP0936279B1 (en) 1997-08-05 1998-08-03 Thick cold rolled steel sheet excellent in deep drawability and method of manufacturing the same

Country Status (10)

Country Link
US (1) US6217680B1 (ko)
EP (1) EP0936279B1 (ko)
JP (1) JPH1150211A (ko)
KR (1) KR100512343B1 (ko)
CN (1) CN1088118C (ko)
BR (1) BR9806088B1 (ko)
CA (1) CA2267363C (ko)
DE (1) DE69832147T2 (ko)
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CN1088118C (zh) 2002-07-24
CN1241220A (zh) 2000-01-12
BR9806088A (pt) 1999-08-24
EP0936279A4 (en) 2004-04-21
DE69832147D1 (de) 2005-12-08
CA2267363A1 (en) 1999-02-18
TW476793B (en) 2002-02-21
KR100512343B1 (ko) 2005-09-05
JPH1150211A (ja) 1999-02-23
DE69832147T2 (de) 2006-04-20
KR20000068708A (ko) 2000-11-25
EP0936279A1 (en) 1999-08-18
WO1999007907A1 (fr) 1999-02-18
US6217680B1 (en) 2001-04-17
BR9806088B1 (pt) 2008-11-18
CA2267363C (en) 2007-01-30

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